Skip to main content

Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

See other formats

480                                 ALASKAN GLACIER STUDIES
are scattered, small deposits of till and stratified deposits throughout Prince William Sound. Several typical ones are described below.
There is a fiat plain of outwash gravels extending westward from Eyak Lake to Orca Inlet. One knob of morainic material rises through it. In the railway cuts near Cordova station of the Copper River and Northwestern Railway, there are fine exposures of the thick stratified gravels, interbedded with lake clays. In the town of Cordova, above the level of this outwash plain, there are deposits of stony till and gravel of considerable thickness. The mantle of ground moraine near Cordova probably extends higher toward the head of the fiord in the mountains, and lower near Prince William Sound and the Pacific.
We have no information regarding the extent of glacial deposits on Hawkins Island, but the relationships of the driftless area on Hinchinbrook Island suggest strongly that parts of this island, also, were not covered at the stage of maximum glaciation. The eastern end, lying in the jaws of two fiords, Orca Bay and Orca Inlet, where great glaciers formerly extended out from the Chugach Mountains, has probably been glaciated to a much greater height than Hinchinbrook Island. The glacial deposits on Hawkins Island, which has no igneous rock in place, include bowlders of coarse granite observed by Schrader and Spencer.1 The geological map by Grant and Higgins2 shows that these must have come from the Chugach Mountains to the northward between Port Gravina and Sheep Bay.
The low forelands on the northern sides of Hinchinbrook and Montague Islands have been glaciated, and, near sea level, bear thick glacial deposits, including both till and outwash, where we have observed them. The peninsula south of Port Fidalgo has a thick, flat-topped terrace of outwash gravels.
An exposure on Latouche Island, seen by us in 1910, was remarkable for the thorough cementation of the till and gravel by iron and copper-bearing waters. This is about 100 feet above sea level along the tramway between the steamer landing and the Bonanza copper mine.
Introduction. The glaciated portion of the Alaskan coast is divisible into three quite distinct physiographic provinces, all notably mountainous, and all supporting numerous glaciers, large and small. The southeasternmost of these is the irregular, fiorded coast below Cross Sound; the northwesternmost, which includes the region west of Controller Bay, is also an irregular, fiorded coast; and the coast between these is a straight, mountain coast, backed by a continuous, lofty mountain range. Yakutat Bay lies near the center of the latter, and Prince William Sound near the eastern end of the second province. The phenomena of present day glaciers and of former glaciation in these three sections present differences of moment and doubtless, ultimately, one of the important results of Alaskan glacier studies will be a consideration and interpretation of these differences. Although a beginning in such a comparative study might even now be made, on the basis of previous work by Russell, Reid, Gilbert, the United States Geological Survey, and others, we will not- at the present time attempt it, but will confine ourselves to a
i Schrader, F. C. and Spencer, A. C., Geology and Mineral Resources of a Portion of the Copper River District, Alaska, House Doc. 546, 56th Congress, 2nd Session, Washington, 1901, p. 81. »PI. H, Bull. 443, TJ. S. Geol. Survey, 1910.